The present invention relates to a method and apparatus for operating a radio communication system for transmission of data among a multitude of base and remote units which employs a frequency hopping technique to minimize interference from external sources and among internal units.
The invention has particular, but not exclusive, utility in the health care environment. The invention allows for the identification of patients and patient-related items, and provides for quick and accurate updating of patient medical and accounting records.
Medical institutions are faced with a competitive environment in which they must improve profitability and yet simultaneously improve patient care. There are several factors which contribute to the ever increasing costs of hospital care. For example, there is an ever increasing amount of paperwork required by nurses, pharmacists and laboratory personnel. In addition, inaccurate recording of drugs, supplies and tests involved in patient care results in decreasing revenues by a failure to fully capture billing opportunities of these actual costs. Inadequate management also results in a failure to provide an accurate report of all costs involved in treating a particular illness. The lack of accurate and rapid transfer of patient information often reduces the accuracy or effectiveness of drug administration and patient care, thereby increasing the duration of hospital stay.
In addition, hospitals and other institutions must continuously strive to provide quality patient care. Medical errors, where the wrong patient receives the wrong drug at the wrong time, in the wrong dosage or even the wrong surgery, are a significant problem for all health care facilities. Many prescription drugs and injections are identified merely by slips of paper on which the patient's name and identification number have been handwritten by a nurse or technician who is to administer the treatment. For a variety of reasons, such as the transfer of patients to different beds and errors in marking the slips of paper, a patient may be given an incorrect treatment. Further, as health care facilities continue to decrease the number of staff personnel as a cost cutting measure, the possibility of personnel errors will most likely increase. Some of these problems have been addressed in U.S. Pat. No. 4,850,009 by Zook, assigned to the assignee of the present invention. The Zook patent describes a portable handheld terminal which includes a data-entry keyboard, a data-entry optical bar code reader and an RF transceiver. The bar code reader and the keyboard can be used to enter data regarding the patient identity, the type of drug to be administered or other information. The information is transmitted to a base transceiver which modulates the information and electronically communicates with a central recordation means such as a CPU. The base transceiver can transmit verifications or other limited information received from the CPU back to the portable handheld terminal. A set of terminals can also be in hard wire electronic communication with the CPU to enter and display data such as billing information. While the system described in the Zook patent is very effective, it is limited by the number of available non-interfering RF channels.
Some attempt has been made to overcome the inherent limitations of radio communications by utilizing spread spectrum technology. In spread spectrum systems, the radio signal is transmitted over a relatively broad band. This results in a lower power per bandwidth (W/Hz) but a broad channel. The low power at any given frequency within the channel lessens the potential for the system to interfere with other systems. At the same time, the broad channel allows a fairly large throughput rate.
The Federal Communications Commission ("FCC") has set aside certain radio frequency bands for low power communications devices using spread spectrum modulation. Current FCC regulations allow spread spectrum technology in the bands of 902-928 MHz, 2400-2483.5 MHz and 5725-5850 MHz. Because components are not readily available in the later two bands, most systems now in use are designed for operation in the 902-928 band. The FCC regulations require no site license but limit power to 1 watt. The most common spread spectrum systems employ direct sequencing methods, in which a signal is spread over a relatively broad band with the hope that frequency-specific interference will be overcome by clear transmissions elsewhere in the broad band. Direct sequencing methods have the advantage of relatively high throughput rates and low external interference problems. However, they use up a broad band, suffer from near-far problems and must have short range to keep under the FCC power limitations. The use of multiple channels can address the near-far problems, but at the cost of increased external interference problems, since each of the multiple channels is then a narrower band. When direct sequencing methods are used with multiple remote transceivers, it is generally necessary to utilize some form of carrier sensing multiple access ("CSMA") technique, in which each remote transceiver queues up to wait for an opening in the base transceiver. Therefore, while the overall transmission rate may be relatively high, the acknowledgement times may be unacceptably slow as the queued up remote units wait their turn for communication with the base transceiver.
Another spread spectrum technology is known as frequency hopping. In frequency hopping, the signal is in a relatively narrow channel as in conventional radio communication, but the channel hops among a predetermined set of frequencies within the spread spectrum. The FCC rules specify various permissible operating parameters for spread spectrum communications using the designated frequency bands such as the rate of frequency hopping and the frequency width and separation. As compared to direct sequencing, frequency hopping has the potential for longer range transmissions (since the limited power is not spread over a broad band) but presents some problems with fast synthesizers and synchronization requirements. Both systems tend to limit frequency specific external interference but in different ways; direct sequencing systems limit frequency specific external interference by spreading the signal over a wide band, while frequency hopping systems limit frequency specific external interference by hopping to a new, interference-free channel periodically. For purposes of the present invention, one of the most important differences is that dividing the spread spectrum into a large number of frequency hopping channels rather than a lesser number of direct sequencing channels results in fairly low throughput per channel but also results in a large number of non-interfering channels. Therefore, the overall throughput can still be high. Moreover, the acknowledgement times are very fast, because at any given time at least one of the large number of channels is likely to be available. This trade-off between throughput rates per channel and channel availability favors frequency hopping for applications with a large number of simultaneous transmissions of small information packets, and favors direct sequencing for applications with a small number of simultaneous transmissions of large information packets.
A frequency hopping technique is described in U.S. Pat. No. 4,850,036 by Smith for use with two-way communications links. Smith uses a fairly slow frequency hopping rate and is limited in its application by parameters that are optimized for two-way voice communication rather than data transmission. In particular, the transmission channel and reception channel are different in order to accommodate the two-way voice communication. Also, the Smith system contemplates remote units being locked to a given control unit without any capacity to choose the best signal from among physically separated control units.